In general terms, a rolling mill comprises, within a supporting stand, at least two working rolls which bear on at least two back-up rolls along a gripping plane. The rolls are carried at their two ends, by means of rolling bearings, in chocks mounted shiftably, parallel to the gripping plane, in apertures provided in each upright of the supporting stand, each chock having two lateral guide faces sliding along corresponding sliding faces formed on the upright of the stand on either side of the chock.
So-called "four-high" rolling mills, comprising two working rolls each bearing on a back-up roll, and so-called "six-high" rolling mills, in which intermediate rolls are interposed between the back-up rolls and the working rolls, are conventionally used. In both cases, the axes of the rolls are placed in the generally vertical gripping plane, but each working roll can also bear in a larger number of intermediate and/or back-up rolls arranged symmetrically on either side of the gripping plane.
To control the thickness of the rolled product and, in particular, to obtain a uniform thickness in the direction transverse to the rolling direction, bending or curving of the working rolls and, if appropriate, of the intermediate rolls is carried out by means of bending devices acting on the chocks of the corresponding roll. The bending device generally consists, for each chock, of two sets of jacks arranged symmetrically on either side of the chock. Moreover, each bearing part of the chock bears on two jacks set axially apart from one another symmetrically on either side of the mid-plane of the rolling bearings of the chock, so that the bending force is effectively distributed over the rolling bearings.
The stand of the rolling mill is symmetrical relative to a mid-plane perpendicular to the gripping plane and corresponding to the mid-plane of the rolled product. The rolls are therefore normally centered on this plane, in relation to which the chocks are arranged symmetrically.
However, it may be advantageous to ensure a shift of some rolls parallel to their axis and in the opposite direction or not, in order to achieve various objectives, such as uniformity of wear of the rolls or control of the planeness or profile of the rolled product.
It can be seen that the axial shift of the rolls presents difficulties when these are subjected to a bending force. Consequently, the two operations are usually carried out separately, the bending force being stopped when an axial shift takes place.
However, it is expedient, during rolling, to combine the effects of axial shift and of bending of the rolls and consequently to make it possible to carry out the axial shift of the rolls while at the same time continuing with bending. Furthermore, the torque is usually exerted on a single pair of rolls, and the bending of the corresponding working rolls takes place as a result of friction. It is necessary that all the rolls should continue to be driven at the same peripheral speed.
Moreover, the bending of the working rolls also ensures a balancing effect between the rolls which it is expedient to maintain during axial adjustment, even when the rolling force is cancelled.